Following the Restoration (and by now a Doctor of Divinity), Barrow received back his fellowship at Peterhouse and was appointed a Fellow of Eton College on 12 July 1660.
On 5 July 1663, having resigned his fellowship of Peterhouse in the previous year, he was consecrated Bishop of Sodor and Man at Westminster Abbey.
By virtue of his establishment in 1668 of the Bishop Barrow Trust, he is generally regarded as the founder of King William's College (where his arms are displayed on the badge), although the school did not open until 1833.
Returning to England for the sake of his health, Barrow lived at Cross-Hall, in Lathom, Lancashire, a house belonging to the Stanley family.
At St Asaph, he again displayed energy and zeal, carrying out substantial repairs to the cathedral church and the episcopal palace, as well as building in 1673 an almshouse for eight poor widows.